As the selection mechanism for single element typewriters is incorporated into the print carrier for machine simplification and reliability, one approach has been to utilize a single translating rack element to provide, selectively, two directions of rotation to the typehead through a rack and pinion arrangement. One illustrative embodiment of this type of mechanism is to be found in Ser. No. 375,277 filed June 29, 1973 in the name of Iraj D. Shakib, titled Single Print Element Print Carrier with Self Contained Selection Function.
The disclosure of this co-pending application, Ser. No. 375,277, is hereby incorporated herein by reference, for an explanation of the mode of operation and structure as disclosed therein.
In the Shakib application, the rack is pivotly mounted and is rocked about its axis of rotation to provide for the engagement and disengagement of the rack teeth with the pinion. This is accomplished by means of, alternatively, electromagnetic or pneumatic elements.
In view of the actions of pneumatic elements only being able to act in one direction, it was necessary that the rack be restored to its home position at the completion of each operation.
The restoration of the rack to its home position at the end of each cycle required a nominal amount of time in each cycle which if eliminated could provide for greater flexibility.
The device disclosed in the Shakib specification, referenced above, required that time be allocated for a restoration of the rack mechanism at the end of each cycle. This allocation of time during any one print cycle restricted the ability to lengthen other operational times during the print cycle and therefore reduced design flexibility. Further, in requiring the time necessary to restore the Shakib mechanism, it, to some extent, restricted and hampered efforts to improve the speed of the mechanism.